Thermoplastic waste converter

ABSTRACT

A method and apparatus for converting thermoplastic waste material into a commercial-grade granular material wherein the waste material is introduced into a chamber containing a rotating cutter which shreds and frictionally heats the thermoplastic material which is thereafter cooled by cooling water added to the material while the cutting operation continues. The cooling water or vapor is then withdrawn or exhausted from the container under negative pressure leaving the granular material dry. Also, solvents are removed from the material. The cutter blade may include baffle bars which provide frictional heating surfaces for heating the thermoplastic waste material.

United States Patent 1 1 Gray et al.

[4 1 July 29, 1975 THERMOPLASTIC WASTE CONVERTER 22 Filed: Nov. 12, 197321 Appl. No.: 414,742

Primary ExaminerRoy Lake Assistant Examiner-DeWalden W. Jones Attorney,Agent, 0r Firm-Pravel & Wilson [57] ABSTRACT A method and apparatus forconverting thermoplastic waste material into a commercial-grade granularmaterial wherein the waste material is introduced into a chambercontaining a rotating cutter which shreds and frictionally heats thethermoplastic material which is thereafter cooled by cooling water addedto the material while the cutting operation continues. The cooling wateror vapor is then withdrawn or exhausted from the container undernegative pressure leaving the granular material dry. Also, solvents areremoved from the material. The cutter blade may include baffle barswhich provide frictional heating surfaces for heating the thermoplasticwaste material.

2 Claims, 4 Drawing Figures PATENTED JUL 2 9 I975 SHEET THERMOPLASTICWASTE CONVERTER BACKGROUND OF THE INVENTION 1. Field of the Invention:

A method and apparatus for converting film form thermoplastic or fiberwaste material such as polypropylene into commerical-grade granularmaterial by shredding and heating the waste material in a container andthereafter cooling the heated material to form it into granules.

2. Description of the Prior Art:

The prior art includes devices such as that of Beck et al, US. lettersPat. No. 3,685,748, which provides a means for pulverizing anddensifying thermoplastic waste into granular form. However, such priorart devices do not process low-density waste plastic material fastenough to be commerically desirable and also do not generate sufficientheat to satisfactorily process high-density thermoplastic wastematerial.

SUMMARY OF THE INVENTION The present invention provides a new andimproved method and apparatus for processing waste thermoplasticmaterial to convert it into commercially usable granules. In oneembodiment of the apparatus of the present invention, the rotatingcutter or blade is provided with baffle bars which frictionally heat thebatch of thermoplastic material to facilitate converting it to agranular form. Further, the present invention is provided with a wateror moisture removal apparatus which effectively separates the coolingwater from the batch after it has been cooled and which also removessolvents from the processed material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an isometric view partly insection which illustrates the apparatus of the present invention forconverting thermoplastic waste material into granular particles;

FIGS. 2 is a top view illustrating the cutter blade used in theapparatus of the present invention;

FIG. 3 is a side view, partly in section, illustrating additionaldetails of the cutter blade; and

FIG. 4 is a partial top view illustrating details of the automatic gatefor controlling removal of moisture and solvents from the container inwhich the batch is converted.

DESCRIPTION OF THE PREFERRED EMBODIMENT The apparatus of the presentinvention is designated generally A in FIG. 1 of the drawings. Suchapparatus A includes a cylindrical drum C for receiving a charge of thematerial to be processed and has a rotating blade or cutter B disposednear the bottom of such drum. A moisture-removable blower or exhaust fanF is provided for removing moisture from the container C as will bedescribed in detail hereinafter. The drum or container C is connectedvia a chute to a hopper H which receives the material after it has beenprocessed in the drum C. With the apparatus of this present invention, abatch or charge of approximately 100 pounds of scrap thermoplasticpolyethylene material is placed in the container C through a suitableopening (not shown) which is preferably positioned adjacent the top ofthe container C. With this apparatus, a batch of waste filmthermoplastic polyethylene is shredded into small strips by high speed(approximately 1800 rpm.) rotation of the cutter blade B adjacent thebottom of the drum or cylindrical container C and thereafter continuedrotation of such blade B frictionally heats the material and therebycauses it to form into particles which are then cooled by injectingwater into the container with continued rotation of the blades. Next,cooling water and vapor is removed from the container through theexhaust fan or blower F and the pulverized granular material suitablydried and then discharged from the container into the hopper H. Also,solvents from any ink released during processing of the wastethermoplastic material are removed by the exhaust blower F.

With the apparatus of the present invention, approximately one hundredpounds of waste thermoplastic material can be shredded, heated andcooled to form granular material having a density of 23 to 25 pounds percubic foot, which is particularly desirable for commercial application.Also, the apparatus of the present invention is suitable for processinghigh-density as well as low-density thermoplastic material.

Considering the apparatus of the present invention in more detail, thecylindrical container C is formed of suitable material such as steelwith a top 11, a bottom 12, and a side wall 13. The bottom 12 rests onsuitable supports 15, 16, 17 and 18, respectively, which support thedrum or container C in an elevated position above the floor. Also, asshown in FIG. I of the drawings, a pair of horizontally extending beamsor runners 19 may be provided which rest on the floor (not shown).

A drive motor 20 is supported beneath the bottom 12 with its shaft 22projecting upwardly through such bottom for connecting the blade B whichis driven by the shaft 22. The motor 20 is preferably an electricalmotor, although other motor devices may be used if desired for rotatingor driving the blade B.

The top 11 is provided with a suitable opening 21 through which passes asuitable discharge pipe 25 that is connected to the exhaust blower fan Ffor exhausting moisture and vapor from inside of the cylindricalcontainer C. The exhaust fan F is connected to a discharge tube 27 whichnormally extends through the wall of a building for discharging themoisture-laden air withdrawn from the chamber or container C to theatmosphere.

As best seen in FIG. 4 of the drawings, a sliding gate designatedgenerally G is provided for opening and closing the discharge conduit25. Such gate includes a horizontally extending gate member 30 whichslides between a pair of vertically spaced plates 32 and 34 which arepositioned adjacent the upper surface of the top 11. The upper plate 34is provided with a suitable opening 34' which corresponds with theopening or passage through the discharge conduit 25. The gate 30 isprovided with an up-turned flange member 30 which is connected to apiston rod 36 of an air or hydraulic cylinder 38 for moving the gate Glaterally with respect to the discharge conduit 25. As shown in FIG. 4of the drawings, the gate 30 is withdrawn or partially open so as topermit partial communication through the con duit 25 and the passage 34.However, it will be appreciated that in normal operation, the gate 30will be either fully opened or fully closed.

The container C is also provided with a lower discharge conduit fordischarging the granular particles of thermoplastic material upon thecompletion of each cycle in the process. Such discharge conduitdischarges the material into the hopper H which may then be used to bagthe material for shipment.

The cutting blade B is shown in more detail in FIGS. 2 and 3 of thedrawings wherein such blade comprises a single plate member 40 which isadapted to be rotated in a counterclockwise direction as seen in FIG. 2of the drawings. Upon rotation in such counterclockwise direction, theblade B is found to have a pair of tapered leading edges 42 and inclinedtapered ends 43. Such inclined tapered ends 43 are inclined a smallamount, approximately from a line perpendicular to the rear or trailingedge on each end of the blade B. Such trailing edge 44 is generallyparallel to the centerline 45 of the blade B. Also as shown in FIGS. 2and 3 of the drawings, a pair of baffle bars 48 are secured to the plate40.

Such baffle bars are preferably set in suitable longitudinally extendingslots or recesses 49 formed or milled in the upper surface of the bladeor plate 40. The baffle bars 48 which are provided for frictionallyengaging the waste material as the blade B is rotated in the cylinder Cto frictionally heat to such material. It has been found that the bafflebars 48 add significantly to the frictional heating effect on thethermoplastic material. As shown in FIG. 3 of the drawings, the bafflebars 48 are secured to the blade plate 40 by screws or bolts 48 and arereplaceable so that different size bars may be used for different typesof thermoplastic material, as desired.

As shown in FIGS. 2 and 3 of the drawings, the blade B is secured to ahub 50 by means of a plurality of screws 52 that are countersunk withtheir heads recessed so as not to project above the top of the plate 40.As shown, the heads of screws 52 are recessed below the upper surface ofthe blade 40. The hub 50 is keyed to the shaft 22 by the key 54 and aplurality of shear pins 55 are provided between the hub 56 and the blade40. In the event the screws 52 work loose, the shear pins will shear sothe shaft will not continue to rotate the blade.

With the apparatus of this invention, waste thermoplastic material whichcan be either low-density or high-density polyethylene can be processed.The low density material has a melting point of approximately 250F andthe high density material has a melting point of approximately 275 to285F. The fast-melt, lowheat material may be run without the bafflebars, however, the high-density PVC is generally run with the largerbaffle bars so as to provide additional friction. After charging thecontainer C with the scrap material to be run, the blade B is rotated soas to cut and heat the scrap material. Thereafter, water is added tocool the material and then the gate is opened so as to expose theinterior of the container C to a back pressure created by the exhaustfan F to remove the moisture from the container C. After the granularmaterial has thus been dried, it is removed into the hopper H forstorage and/or bagging.

Also, it has been found that with the method and apparatus of thepresent invention, sufficient solvents are removed from printed materialso that its subsequent use does not require a vented extruder.

It has been found in using the apparatus of the present invention toprocess the waste thermoplastic the following steps or sequence may bebeneficially employed. It will be understood that the times andmeasurements which are set forth herein are approximations andsubstantial conformity thereto will produce the desired results.

First, the container C is loaded with an initial start-up batch ofthermoplastic material. In a period of approximately thirty secondsabout thirty pounds of material can be inserted into the machine. Thisis done with the machine running, and therefore, the blade immediatelybegins cutting the material. An ammeter is provided with the machine andconnected in the circuit which supplies current to operate the electricmotor to drive the blade, and by observing the ammeter, it will be seenthat the ammeter runs up during the loading process and drawsapproximately 180 amps for the 150 horsepower electric motor used in thepreferred embodiment of this invention. After a period of approximately1 minute, the balance of the load which will be another to pounds isadded to the machine, which requires approximately an additional minuteduring which time the blade will be cutting the additional wastematerial into shredded pieces.

For a period of 45 seconds after the total load has been placed in themachine, the blade continues to run and heats the material which by thistime has been substantially shredded. This is indicated by a drop in theammeter reading which occurs during the cooking cycle and the ammeterdrops to approximately amps where it generally remains throughout thecooking cycle, which is a term designating this 45 second periodfollowing the completion of placing the full load in the machine.Approximately half-way through this cooking cycle of 45 seconds, a smallamount of water, say 16 ounces, is sprayed into the container in whichthe material is being processed. Thereafter, an additional quart ofwater is added at the end of the cooking cycle and, after approximately5 seconds following the addition of that quart of water, an additionalspray is injected into the batch to cool and coagulate the thermoplasticmaterial. The additional spray may be as much as 16 to 32 ounces ofwater. About 5 seconds after the cooling has been completed, the exhaustblower is employed to remove moisture from the thermoplastic material inthe tub or container C. The negative pressure created by the exhaust isimposed on the contents of the drum for approximately 30 seconds oruntil all the moisture has been cleared. Thereafter, the dry granulatedmaterial is dumped from the container C into the hopper H or othersuitable container, which requires approximately 15 seconds, after whichtime the discharge door is closed and the cycle is repeated.

Also, in the preferred embodiment of this invention, it has been foundthat it is advantageous to position the blade B approximately 1% inchesabove the bottom of the container C with the ends 43 of the rotatableblade 40 spaced below the plurality of laterally extending fixed blades60 which are spaced circumferentially around the container C and whichproject radially inwardly. The inner ends 61 of the blades 60 extendinwardly so as to overlap the ends 43 as shown in FIG. 3.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof, and various changes in the size,shape and materials as well as in the details of the illustratedconstruction may be made without departing from the spirit of theinvention.

We claim:

1. A method of processing thermoplastic film material to convert it intogranular form, comprising the steps of:

a placing a first batch of approximately thirty pounds of thermoplasticfoil material into a container having a cutting blade rotating thereinat a speed of approximately 1800 rpm;

b. placing a second batch of approximately seventy to eighty pounds ofthermoplastic foil material in said container approximately one minuteafter said first batch is placed in said container with said bladecontinuing to rotate in said container;

0. rotating said blade in said container for a period of approximately22 seconds after said second batch is placed in said container;

d. thereafter, spraying approximately sixteen ounces of water into saidcontainer and continuing to retate said blade for another period ofapproximately 23 seconds;

e. injecting approximately one quart of water into the container withthe blade continuing to rotate;

f. rotating said blade for an additional period of approximately 5seconds following the addition of the quart of water;

g. spraying approximately 16 to 32 ounces of water into said containerto cool the batches of thermoplastic material therein;

hi applying a negative pressure to the container to exhaust moisture andgases therefrom;

i. discharging the dry, granulated, processed material from thecontainer.

2. In an apparatus for converting thermoplastic foil 5 material intogranulated thermoplastic, including:

a. a cylindrical container having a top and a bottom;

b. motor means mounted below said bottom for rotating a shaft extendingthrough said bottom and disposed substantially axially of saidcylindrical container;

c. a plurality of circumferentially spaced fixed blades mounted at thewall of said cylinder and projecting radially inwardly and above thebottom of said cylinder, the improvement comprising:

a rotatable blad member mounted on the shaft of said motor and extendingdiametrically of said cylinder below said fixed blades, said rotatableblade member having sharpened leading cutting edges on opposite sides ofsaid shaft for cutting thermoplastic material in said cylinder and saidsharpened leading edge being inclined with respect to the center line ofsaid blade member; further said rotatable blade having a sharpenedcutting edge extending along each end of said blade member and taperedoutwardly and rearwardly of said leading cutting edge.

1. A METHOD OF PROCESSING THERMOPLASTIC FILM MTERIAL TO CONVERT IT INTOGRAULAR FORM COMPRISING THE STEP OF: A. PLACING A FIRST BATCH OFAPPROXIMATELY THIRTY POUNDS OF THERMOPLASTIC FOIL MATERIAL INTO ACONTAINER HAVING A CUTTING BLADE ROTATING THEREIN AT A SPEED OFAPPROXIMATELY 1800 R.P.M, B. PLACING A SECOND BATCH OF APPROXIMATELYSEVENTY TO EIGHTY POUNDS OF THERMOPLASTIC FOIL MATERIAL IN SAIDCONTAINER APPROXIMATELY ONE MINUTE AFTER SAID FIRST BATCH IS PLACED. INSAID CONTAINER WITH SAID BLADE CONTINUING TO ROTATE IN SAID CONTAINER,C. RROTATING SAID BLADE IN SAID CONTAINER FOR A PERIOD OF APPROXIMATELY22 SECONDS AFTER SAID SECONDD BATCH IS PLACED IN SAID CONTAINER,
 2. Inan apparatus for converting thermoplastic foil material into granulatedthermoplastic, including: a. a cylindrical container having a top and abottom; b. motor means mounted below said bottom for rotating a shaftextending through said bottom and disposed substantially axially of saidcylindrical container; c. a plurality of circumferentially spaced fixedblades mounted at the wall of said cylinder and projecting radiallyinwardly and above the bottom of said cylinder, the improvementcomprising: a rotatable blad member mounted on the shaft of said motorand extending diametrically of said cylinder below said fixed blades,said rotatable blade member having sharpened leading cutting edges onopposite sides of said shaft for cutting thermoplastic material in saidcylinder and said sharpened leading edge being inclined with respect tothe center line of said blade member; further said rotatable bladehaving a sharpened cutting edge extending along each end of said blademember and tapered outwardly and rearwardly of said leading cuttingedge.